Many devices have heretofore been proposed for analysis of the breath, especially the deep lung or alveolar air, of persons suspected of drunk driving. Some of these devices have attained significant acceptance with the police and the courts, and are generally respected aids to traffic law enforcement. The amount of alcohol in the breath is proportional to the amount of alcohol in the blood; hence, breath testing provides reliable chemical evidence of the level of intoxication.
In accordance with our aforesaid parent application, we have discovered that a breath sample may be obtained in a reliable and convenient manner by the use of a partially evacuated valved canister having an inlet tube with a pressure relief valve. The suspect is required to blow into the tube for a period of time, and then the valve of the canister is opened, which draws a predetermined volume of the suspect's breath into the canister.
After the breath sample has been obtained, quantities of the sample may be withdrawn from the canister for testing. The amount of alcohol present in the sample may be determined by various methods, some of which involve comparison of the sample against a known quantity of alcohol.
Frequent calibration checks on the testing instrument are also necessary to render the results legally sufficient and to show that the instrument or other testing device was performing properly at the time the test was made. Any alcohol standard employed in connection with such tests must obviously be reliable and convenient to use without error on the part of the instrument operator. The possibility of a contaminated or unreliable alcohol standard will obviously undermine the validity of the test.